The volume of data now exchanged through telecommunications networks requires data networks having a high data transfer capacity. Such networks must also serve large geographical areas. Network scalability to achieve a very high-capacity and wide-area coverage may be realized by increasing the number of nodes in a network and/or increasing the transfer capacity per node. For a given link capacity, e.g., 10 Gb/s, increasing the capacity per node necessitates increasing the number of links per node. In a balanced network, the mean number of hops per node pair is inversely proportional to the number of links per node. Decreasing the mean number of hops per node pair dramatically reduces network-control complexity, facilitates the routing function, and enables the realization of network-wide quality of service (QOS) objectives.
In order to decrease the number of hops per node pair in a network, very high-capacity switches are required. Consequently, methods are required for constructing very high-capacity switches. It is also desirable that such switches be distributed to permit switch access modules to be located in proximity of data traffic sources.
Advances in optical switching technology have greatly facilitated the construction of high-capacity switches using optical space switches in the switch core. The principal problem encountered in constructing high-capacity switches, however, is the complexity of coordinating the transfer of data between ingress and egress, while permitting the creation of new paths between the ingress and the egress. Consequently, there exists a need for a method of increasing data transfer capacity while simplifying data transfer control in a high-speed data switch.
The design of data switching systems has been extensively reported in the literature. Several design alternatives have been described. Switches of moderate capacity are preferably based on a common-buffer design. For higher capacity switches, the buffer-space-buffer switch and the linked-buffers switch have gained widespread acceptance. A switch based on an optical space-switched core is described in U.S. Pat. No. 5,475,679 which issued on Dec. 12, 1995 to Munter. An optical-core switching system is described in U.S. Pat. No. 5,575,320 which issued May 19, 1998 to Watanabe et al.
A buffer-space-buffer switch, also called a space-core switch, typically consists of a memoryless fabric connecting a number of ingress modules to a number of egress modules. The ingress and egress modules are usually physically paired, and an ingress/egress module pair often shares a common payload memory. An ingress/egress module pair that shares a common payload memory is hereafter referred to as an edge, module. The passive memoryless fabric is preferably adapted to permit reconfiguration of the inlet-outlet paths within a predefined transient time. The memoryless core is completely unaware of the content of data streams that it switches. The core reconfiguration is effected by either a centralized or a distributed controller in response to spatial and temporal fluctuations in the traffic loads at the ingress modules.
The linked-buffers architecture includes module sets of electronic ingress modules, middle modules, and egress modules, and has been described extensively in the prior art. Each module is adapted to store data packets and forward the packets toward their respective destinations. The module-sets are connected in parallel using internal links of fixed capacity.
The control function for the linked-buffers switch is much simpler than the control function for the space-core switch. The capacity of the linked-buffers switch is limited by the capacity of each module-set, the number of internal links emanating from each ingress module, and the number of internal links terminating to each egress module. With a given module-set capacity, the capacity of a linked-buffers switch can be increased virtually indefinitely by increasing the number of internal links, which permits the number of module-sets in the switch to be accordingly increased. However, with a fixed module capacity, when the number of internal links is increased, the capacity of each internal link must be correspondingly reduced. Reducing the capacity of an internal link is not desirable because it limits the capacity that can be allocated to a given connection or a stream of connections. A switch with a space switch core does not suffer from this limitation.
The linked-buffers switch can be modified in a known way by replacing a module-set with a single module having a higher capacity than that of any of the modules in the module set. As described above, a module set includes an ingress module, a middle module, and an egress module. The modified configuration enables both direct and tandem connections between ingress and egress and is hereafter referred to as a mesh switch. The mesh switch enables direct switching from ingress to egress as well as tandem switching.
A disadvantage of the switching architectures described above is their limited scalability.
Prior art switches may be classified as channel switches that switch channels without examining the content of any channel, and content-aware data switches. A switched channel network has a coarse granularity. In switched data networks, inter-nodal links have fixed capacities. Consequently, fluctuations in traffic loads can require excessive tandem switching loads that can reduce the throughput and affect network performance.
There therefore exists a need for a self-configuring data switch that can adapt to fluctuations in data traffic loads.